An innovative Theory of Perceptual Media predicts which stimulus attributes are necessary for the existence of Gestalt phenomena. The proposed research on pre-attention will investigate perceptual organization in pitch and spatial frequency: in particular it will focus on segregation of one pitch from concurrent pitches, and one spatial frequency from concurrent spatial frequencies. The theory also suggests differences between attending to a region of a perceptual medium and to a region of some other attribute. In order to test this implication the two types of attention will be compared.